How to create many-to-many relationships with Objectify in the Google App Engine?

Question

I cannot find any documentation on the appropriate way to make many-to-many relationships between objects using Objectify in the Google App Engine.

Can someone explain how to do this? Do I need to create a new class for this? How effective is it?

Answer 1

What queries do you need for support?

The simplest solution:

@Entity
public class StoredObject {
    @Id
    private Long id;

    private List<Long> relatedIds;
}

then with a StoredObjectyou can call objectify.get(StoredObject.class, storedObject.getRelatedIds())to get all associated identifiers.

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Answer 2

Objectify. - , . , , A B, . , :

Class Link{
    Key<?> master;
    key<?> slave;

    public Link(){

    }

    public setLink(Entity master, Entity slave){
     //initialize

    }

}

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Answer 3

Objectify 4.0:

@Entity
@Index
public class Module {

@Id
private Long id;
private String name;

@Load
private List<Ref<Template>> templates;


public List<Template> getTemplates() {
    List<Template> templates = new ArrayList<Template>();

    for (Ref<Template> temp : this.templates) {
        templates.add(temp.get());
    }

    return templates;
}

public void setTemplates(List<Template> templatesParm) {
    List<Ref<Template>> templates = new ArrayList<Ref<Template>>();

    for (Template temp : templatesParm) {
        templates.add(Ref.create(temp));
    }

    this.templates = templates;

}

Answer 4

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• NoSQL/ObjectStore: make A , () B-s. , B-s ( GAE/Java .)

. ObjectStore . , , A B Entity Group, Ancestor (, , ), Bs, A. A Bs , (, , ), B, , B, : https://developers.google.com/appengine/articles/transaction_isolation

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